Numerical calculations in the orbital determination of an artificial satellite for a long arc     

Lin Liu  Xinhao Liao 《Celestial Mechanics and Dynamical Astronomy》1994,59(3):221-235

Numerical methods are usually used for the computation of ephemerides with perturbations for the precise orbital determination of an artificial satellite. But their numerical stability will be encountered in a long arc. In this case the use the improved Encke special perturbation methods has been suggested. The results of this paper show that Encke's method does indeed have a certain effectiveness, but cannot yet completely resolve the numerical stability, and the more efficient method is to use the energy integral or its variational relation to control the growth of the along-track error in general numerical calculations so that the aim of stabilization can be achieved.  相似文献   

广东省拖网网囊调查     

杨吝  张旭丰  孙典荣  谭永光 《广东海洋大学学报》2001,21(4):22-26

为实施中华人民共和国国家标准《南海区拖网网囊最小网目尺寸》,对广东省范围内拖网网囊现状进行摸底调查,结果表明,广东省沿海拖网渔船现用网囊网目尺寸(内径)在16.7～35.2 mm范围内,总体平均为27 mm,均未能达到1989年国家技术监督局发布的中华人民共和国国家标准--《南海区拖网网囊最小网目尺寸》--内径39 mm.  相似文献   

Effective collision strengths with inclusion of resonance for hyperfine-structure transitions in H- and Li-like ions     

Hong Lin Zhang  Douglas H. Sampson 《Monthly notices of the Royal Astronomical Society》2001,322(3):433-437

Calculations are made of the resonance contribution to electron-impact excitation of H-like ¹³C and Li-like ²³Na, ²⁵Mg, ²⁷Al and ²⁹Si to the upper hyperfine levels that produce millimetre (mm) lines of likely astrophysical interest. The resonance contribution is found to be very important for these Li-like ions, considerably more important than for Li-like ⁵⁷Fe considered previously. However, resonances are found to be rather unimportant for H-like ¹³C. The effect of radiative decay on the resonance contribution is found to be insignificant in all of the present calculations.  相似文献   

A concordance model of the Lyman α forest at z= 1.95     

Tridivesh Jena  Michael L. Norman  David Tytler  David Kirkman  Nao Suzuki  Angela Chapman  Carl Melis  Pascal Paschos  Brian O'Shea  Geoffrey So  Dan Lubin  Wen-Ching Lin  Dieter Reimers  Eckardt Janknecht  Cora Fechner 《Monthly notices of the Royal Astronomical Society》2005,361(1):70-96

  相似文献   

在社会发展的层面上认识“数字地球”   总被引：1，自引：0，他引：1  

郭仁忠  林亨贵 《地球信息科学学报》2001,3(1):50-53

 本文讨论了“数字地球”的有关问题。指出“数字地球”是人类社会及其活动在网络空间的延伸和拓展,是信息技术带来的社会发展趋势。关于“数字地球”的讨论不应局限在空间信息技术领域,而应该在社会发展的层面上认识它  相似文献   

调频式电涡传感器微机实现的探讨     

林菁 《广东海洋大学学报》1996,(1)

分析了分频和ＣＴＣ计数采样中误读数的原因和解决方法，并利用微机软件实现非线性校正。此传感器用于位移测量系统中，具有０．０１ｍｍ的分辨率及优于１％的精度，可在－２０～６０℃温度范围内工作。  相似文献   

Fracture energy release and size effect in borehole breakout     

Zdenk P. Baant  Feng-Bao Lin  Horst Lippmann 《国际地质力学数值与分析法杂志》1993,17(1):1-14

The paper presents a simple approximate analytical solution of the remote stresses that cause the collapse of a borehole or other circular cylindrical cavity in an infinite elastic space. Regions of parallel equidistant splitting cracks are assumed to form on the sides of the cavity. Their boundary is assumed to be an ellipse of a growing horizontal axis, the other axis remaining equal to the borehole diameter. The slabs of rock between the splitting cracks are assumed to buckle as slender columns, and their post-critical stress is considered as the residual stress in the cracked rock. The buckling of these slab columns is assumed to be resisted not only by their elastic bending stiffness but also shear stresses produced on rough crack faces by relative shear displacements. The energy release from the infinite medium caused by the growth of the elliptical cracking region is evaluated according to Eschelby's theorem. This release is set equal to the energy dissipated by the formation of all the splitting cracks, which is calculated under the assumption of constant fracture energy. This yields the collapse stress as a function of the elastic moduli, fracture energy, ratio of the remote principal stresses, crack shear resistance characteristic and borehole diameter. The collapse stress as a function of crack spacing is found to have a minimum, and the correct crack spacing is determined from this minimum. For small enough diameters, the crack spacing increases as the (4/5)-power of the borehole diameter, while for large enough diameters a constant spacing is approached. In contrast to plastic solutions, the breakout stress exhibits a size effect, such that for small enough diameters the breakout stress decreases as the (? 2/5)-power of the borehole diameter, while for large enough diameters a constant limiting value is approached. Finally, some numerical estimates are given and the validity of various simplifying assumptions made is discussed.  相似文献   

地倾斜台站数字化、模拟观测数据频率特性研究   总被引：2，自引：2，他引：0  

李正媛  陈鹏  林穗平  陈志遥 《大地测量与地球动力学》2003,23(1):74-77

分析了四川、云南的部分地倾斜数字化观测与模拟观测资料的特性，从频率范围，周期10天以上的FFT谱特性，固体潮波振幅，相位特征值等方面，论述了地倾斜数字化资料较模拟记录资料的信息组成变化，并对资料的分析与应用进行了初步探讨。  相似文献   

丽江高美古台址和2m级望远镜项目(英文)     

陈东  王建成  许骏  罗国权  谭徽松  刘忠  张柏荣 《天文研究与技术》2003,(Z1)

自 1992年起云南天文台开始了在云南省西北部的天文选址。丽江高美古最终被选择作为未来中国地基天文光学观测的新址点。并且 ,在国家科技部 ,云南省政府 ,以及中科院的支持下 ,2m级天文望远镜项目在 2 0 0 0年 12月获得立项。在文中 ,我们简要的介绍了高美古台址的情况 ,并给出了 2 .4m望远镜的详细情况 ,以及其他相关情况。  相似文献   

澳门附近海域沉积物污染状况及特征分析     

张和庆  谢健 《广东海洋大学学报》2003,23(3):39-44

掌握澳门附近海域沉积物的污染状况及特征,对于合理安排澳门海洋海岸工程疏浚泥的海洋倾倒,防止造成海洋污染有十分重要的意义。根据1997—1999年连续三年对澳门附近主要区域的海洋沉积物采样测定结果,通过分析认为澳门附近海域沉积物污染具有下列特征:1)沉积物中重金属和油类含量普遍较高,除了总Hg外均高于珠江口海区的其他港口;2)沉积物中污染物的分布受人类活动的影响明显,澳门内港受船只排污、码头作业、陆地工业和生活污水排放的影响,是澳门附近海域沉积物污染最为严重区域;3)受水质交换的影响明显,澳门外港、路环岛东北等区域受珠江径流影响水质交换较快,沉积物中污染物的含量较低,而内港由于水质交换较差,沉积物中污染物的含量相对较高;4)与沉积物的成分组成(吸附)有关,大部分污染物与沉积物中粉砂有较好的相关性,表明粉砂对污染物质有较广泛性的吸附能力,尤其是Cu、Zn、Cd、油类、有机质。  相似文献